Patent Application
20220274172
This disclosure relates to three dimensional printing of parts. Specifically, this disclosure relates to systems and methods to reduce distortion in a three dimensional printed part during a subsequent heating operation, such as debinding, sintering, and/or increasing density.
The accompanying drawings illustrate various examples of the principles described herein and are a part of the specification. The illustrated examples do not limit the scope of the claims.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated and/or minimized to more clearly illustrate the example shown. The drawings provide examples and/or implementations consistent with the description. However, the description is not limited to the examples and/or implementations shown in the drawings.
Forming three-dimensional printed parts from metal rather than polymer provides a number of benefits. Metals allow material properties not found in polymers and other types of materials. Metals may have break strength, ductility, conductivity, yield strengths, and other properties that are difficult to reproduce with polymers and ceramics. The rise of engineering polymers such as polyetheretherketone (PEEK) have increased the options for polymers but engineering polymers may have limited strength, ductility, and conductivity. Accordingly, metal parts will continue to be used in various applications for the foreseeable future.
Metal parts have generally been made with machining and/or casting. Swiss and computer numerical control (CNC) mills may be used to automate or semi-automate production of small metal parts. However, such systems tend to be operated on a setup-and-let-run model rather than an on-demand approach. In contrast, printing of parts has been seen as a method of providing parts on demand while allowing a high degree of customization of a given part. Printing parts also allows formation of geometries which may be difficult and/or impossible to form with other methods.
Three dimensional forming of metal parts may include applying a binder to metal particles to form a green part. The green part is then heated. During heating, the binder is removed, for example, by volatilization and/or combustion. The part is sintered together to form a solid object. In some examples, the part is further heated to densify the metal part.
When loosely packed, metal particles may have a density of less than 50% of their consolidated density. Vibration and mechanical packing may be used to increase the density of the particles prior to heating. However, even under optimal conditions, the metal particles will more resemble spheres than cubes. This results in interstitial space between particles that is occupied by air, reducing the density of the part.
In some 3-D metal part processes, post-forming heating includes a first temperature where a binding agent is removed, a higher second temperature where sintering occurs and a third even higher temperature where densification happens. However, there is a challenge in that once the binding agent is removed, the binding agent no longer provides support for the 3-D formed shape. As the part is heated to sintering temperature, the part may sag, deform, and/or collapse. Sagging, collapse and/or deformation may become even more severe during densification.
Densification also produces shrinkage, i.e., a reduction in dimensions for the part, as the empty areas between particles are filled by mobile metal atoms at elevated temperature. However, reduction in metal strength at temperatures needed for sintering may cause undesired deformation of the part, in addition to unavoidable shrinkage. Densification may include higher temperatures than sintering and may include liquefaction of some metal in the part.
As used in this specification and the associated claims, a “green part” is a part formed from particles which requires a thermal process before finalization. A green part may include a binder which is chemically and/or thermally removed (debind) as part of post forming processing. A green part may be subjected to a sintering and/or densification process as the secondary process. The term “green part” is used in the field of powder metallurgy.
As used in this specification and the associated claims, “debind” is the process of thermally and or/chemically removing a binding agent from a green part. Such binding agents are often organic and are either decomposed and/or combusted. Binding agents may hold the green part in its formed shape during forming and post-forming operations. For example, a binding agent may hold the green part together during removal of excess material in layers of the formed structure that will not become part of the green part.
As used in this specification and the associated claims, “sintering” is the process of bringing a material to a temperature sufficient to allow diffusion of the material into adjacent material without liquefaction. The adjacent material may be the same and/or different material. Sintering may include a debind operation, a consolidation operation, and/or a densification operation. In an example, an initial sintering is performed to increase the strength of the part, the support may then be removed and a secondary sintering performed to further consolidate the part.
This specification also describes a system for forming a part with a support including: a liquid reservoir to hold a support material to form the support; an ejector to receive support material from the liquid reservoir and deposit the support material into a build area; an actuator to provide relative motion between the ejector and the build area; and a spreader to form a layer of metal particles in the build area, wherein the support provides support for the part during sintering.
Among other examples, this specification also describes a system for forming a part with a support, the system including: a first liquid reservoir to hold a support material to form the support; a first ejector to deposit the support material into a build area; a second liquid reservoir to hold a binding agent; a second ejector to deposit the binding agent into the build area; an actuator to provide relative motion between the first ejector and the build area; and a spreader to form a layer of metal particles in the build area, wherein the support material comprises an oxide and the support provides support to the green part during sintering.
Among other examples, this specification also describes a method of forming a metal part, the method including: forming, by layers, a metal part and a support for the metal part; and sintering the metal part while the metal part is supported by the support.
Turning now to the figures,
The system (100) is a system (100) for forming a support and a part during the same layer-by-layer forming process. This is done by providing a support material in a liquid reservoir (110) where the support material may be applied to form a support structure in a build area (130).
The liquid reservoir (110) contains support material that will become the support structure. The liquid reservoir (110) provides liquid to the liquid ejector (120).
The support material forms the support in the build area (130). The support provides support to the part during a subsequent thermal operation. The thermal operation may be debind, sintering, densification, and/or another thermal operation on the part. The part may include a binder. The part may be substantially free of binder, for example, having less than 1%, 0.1%, 0.01%, and/or 0.005% by weight of binder.
The support material may be a material selected from a group consisting of: alumina, silica, silicates, zirconia, titania, MgO, and mixtures thereof. The support material may include a clay. The support material may include a metal oxide. The support material may include a transition metal oxide. The support material may include a semimetal oxide and/or a non-metal oxide. Oxides tend to be thermally stabile due to their low potential state. The support material may include a ceramic precursor. The support may lack crack propagation resistance and/or overall strength. Indeed, the lack of such characteristics may make removal of the support easier after the support is no longer needed. The support material may be designed to undergo a structural change during heating.
The support material may include a polymer. Polymers with high decomposition temperatures may be particularly useful in this regard. For example, silicones are available in shelf-stable formulations and have notable temperature resistance compared with carbon-based polymers. Silicones may also be formulated to produce a wide variety of stiffnesses from floppy low stiffness materials to highly-crosslinked, firm silicones. The availability of silicone precursors and well understood kinetics of crosslinking make these attractive options for a support material.
The support material may include an ultraviolet (UV) curable polymer such as: an epoxy acrylate, aliphatic urethane acrylate, aromatic urethane acrylate, polyester acrylate, and/or acrylic acrylate. The support material may include a photopolymerizable polymer. The support material may include a thermosetting polymer, for example to bolster the strength of a ceramic shell. Some suitable thermosetting polymers include: polyurethanes, diallyl-phthalates, cyanate esters, polycyanurates, and/or epoxy resins.
The support material may be a ceramic powder ink and may contain (UV) curable component. In an example the UV curable component is activated and hardened while printing each layer.
The support material may be applied to the layer of metal particles as shown in
The part may include a binder. The part may be formed without a binder. The part may have the binder removed during debind prior to sintering. The part may be subjected to an initial sintering, followed by removal of the support prior to a secondary sintering. The support may remain in place until the part has completed all its thermal operations.
The build area (130) is located in the path of the ejected material from the liquid ejector (120). The liquid ejector (120) may be located above the build area (130) to minimize the deflection from gravity. The liquid ejector (120) may be part of a printhead. In an example, the liquid ejector (120) and reservoir (110) are integrated into a single unit. The reservoir (110) may be replaceable. The reservoir (110) may include a port for refilling. The reservoir (110) may supply multiple liquid ejectors (120).
The actuator (140) provides relative motion between the liquid ejector (110) and the build area (130). In an example, the print area (130) is static and the actuator (140) moves the liquid ejector (120) in X and/or Y. The actuator may move the liquid ejector (120) in X, Y, Z, another axis, and/or combinations thereof. Full width liquid ejectors (110) provide an option to limit motion of the system. Actuator (140) systems may be used to move the build area (130) in X, Y, Z, and/or another axis. Both the liquid ejector (120) and the build area (130) may be moved simultaneously and/or separately to facilitate operations. All these combinations for relative motion between the liquid ejector (120) and the print area (130) are within the disclosed scope of this application.
The system (100) includes a spreader (150) to form layers of metal powder in the build area (130). A spreader (150) may include a blade. A spreader (150) may include a roller. A spreader (150) may deposit metal powder as part of forming the layer of metal powder. A spreader (150) may have another system provide the metal powder to the build area (130) while the spreader rearranges the supplied metal powder to form the layer. The spreader may remove excess amounts of metal powder when forming a layer of metal powder. The excess metal powder may be reused.
The spreader (150) may include a compactor to compact the powder layer. The spreader (150) may include a vibrator to compact the powder layer. The spreader (150) may be integrated with the liquid ejector (120) on a common carriage. The spreader (150) may move relative to the liquid ejector (120). Different designs have associated tradeoffs in terms of throughput, parts, reliability, cost, etc.
The spreader (150) may be used to form powder layers of a fixed thickness. The spreader (150) may form layers of different thickness through a build and/or between builds. Again, more flexibility tends to be associated with greater mechanical complexity which may be associated with greater costs and/or reduced mean time to failure for a device.
The system (100) may include a second reservoir (110) and a second liquid ejector (120). This second liquid ejector (120) may be used to dispense a binding agent on the layer of metal powder in the build area (130). The first and second reservoirs (110) and first and second liquid ejectors (120) may be integrated into a single printhead. The first and second liquid ejectors (120) may be in separate printheads and/or on separate carriages. The first and second liquid ejectors (120) may operate simultaneously and/or sequentially to apply the materials from the first and second reservoirs (110).
The support may include a shell. A shell is a support that enrobes and/or covers a majority of a surface of the green part. A shell may have openings, such as vents to allow escape of the binding agent during debind. The shell may be formed from a material which is brittle compared with the part such that the shell may be fractured to facilitate removal from the part. For example, the support may be a ceramic shell encompassing the part. The support may include a vent to allow outgassing during heating of a green part supported by the support.
The support may have a non-uniform thickness. A non-uniform thickness support may provide different levels of support to different portions of a part formed from the layer of metal particles. For example, the base of the support may be thicker than a top portion. Similarly, any non-uniformity may have the thickness and shape of the support designed to provide the desired support of the part, facilitate removal of the support after heating, and/or minimize deformation of the part during heating. The support may include a lower surface. In an example, a base for the support is produced using the same methods as forming the sides of the support. In an example, a base is prefabricated to speed production.
The support may include a lower surface and side walls. The support may include only sidewalls. The support may include a top surface. In some cases, it is advantageous to leave open the upper surface of the support. In contrast, providing support underneath the part is often useful as the part will tend to distort downward under gravity. Similarly, providing lateral support with a wall or walls may prevent the part from flowing outward or folding over during heating. The support may include a prefabricated base. The support may have a base which is fabricated as part of making the support.
In
In an example, the blade forming the layer of metal powder and the liquid ejector (120) for depositing the support material are on a common carriage. The blade may precede the liquid ejector (120), leveling the layer ahead of deposition of the next layer of the support material. The use of a common carriage for both may reduce the number of parts in the system (100). The use of a common carriage may reduce the time per layer as both leveling and deposition occur simultaneously. Multiple carriages may be coordinated to function simultaneously on different portions of the build area (130). This provides additional order of operation and speed flexibility in exchange for more parts in the system (100).
As discussed with respect to
Forming the support from an oxide allow the use of materials with high temperature tolerances. In an example, the working temperature of the support material is above the melting temperature of the metal powder used to form the part. For example, silica may remain functional at temperatures up to approximately 1600° C. which is above the melting point of iron. Zirconia (zirconium dioxide) has a melting point of approximately 2,715° C. which is well above the melting temperature of many metals. Accordingly the selection of a proper oxide to form the support allows the support to function at sintering and densification temperatures. Silicone rubbers and organic polymers may be stable to about 800° C. before decomposing. This may be sufficient for the initial debind and/or sintering depending on the composition of the part.
The method is a method of forming a metal part. The method (500) includes forming a part and an associated support together layer by layer. The support then provides support to the part during sintering. The part may be a green metal part. The support may provide support during debind.
The method (500) includes forming, by layers, a metal part and a support for the metal part (560). By forming the support and the metal part together, the support can be produced in contact with the metal part and provide variable amounts of support to different portions of the metal part. If the support material and binder are provided by fluid ejectors (120) mounted on a common carriage, the additional time to form the support may be minimized. The support can be made using a variety of different materials however; metal, semimetal, and/or nonmetal oxides such as silica, silicates, alumina, titania, zirconia, etc. provide high temperature tolerances. Similarly, ceramic materials have a long history in high temperature use.
The use of polymers provides supports that are useful for lower melting point metals. Polymers have commercially-available, shelf-stable formulations. However, polymers also have less tolerance of higher temperatures.
The method (500) includes sintering the metal part while the metal part is supported by the support (570). As discussed previously, the support stabilizes the metal part to reduce sagging, bending, etc. Deformation of the part may occur during sintering. Deformation of the part may occur during densification. Deformation of the part may occur during debind. Accordingly, the use of a temperature resistant support facilitates stabilization of the part and reduces the stresses that might produce deformation.
The method may further include heating a green part, while the part is supported by the support, during debind. The support may include vents and/or openings to allow gas formed from the binder to escape. The method (500) may further include heating the part to sintering temperature. The method (500) may further include heating the part to densify the part. The method (500) may further include removing the support from the metal part after heating. In an example, the support is fractured and removed from the part as pieces.
The method (500) may further include removing the support from the sintered metal part prior to a second sintering operation. For example, additional densification may be performed after removal of the support.
The support is distinguished from the metal part itself by being formed of a different material and removed after the usefulness of the support in providing support is complete. The support may be removed to prevent the support for interfering with the expected use of the metal part. The support may be recyclable. The support may be disposable. Depending on the adhesion between the support and the part, additional finish methods may be used to separate the part from the support. For example, mechanical vibration, sandblasting, shot peening, chemical etching, and/or similar methods may be used. Selecting an appropriate support removal will depend on the material of the support, the adhesion between the support and the part, and the desired finish of the part itself. In some examples, removing the support may be accomplished as part of other surface finishing operations so as to not increase the time and/or number of processes used to finish the metal part.
It will be appreciated that, within the principles described by this specification, a vast number of variations exist. It should also be appreciated that the examples described are only examples, and are not intended to limit the scope, applicability, or construction of the claims in any way.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 16606299 | Oct 2019 | US |
| Child | 17748414 | US |
